Steerable or deflectable tip cardiovascular catheters are useful in many applications, being a marked improvement over catheters with fixed tips. They are especially useful in the field of electrophysiology for performing radio-frequency ablation of cardiac tissue to interrupt abnormal electrical pathways in the heart. Typically, ablation catheters carry one or more electrodes at their distal end. A steerable catheter assists the physician in guiding the distal end of the catheter so that the electrodes can be properly aligned with the tissue to be ablated.
There are presently several useful designs for steerable tip catheters. Such a catheter generally has a control handle at its proximal end for controlling deflection of the tip in one or more directions. For example, U.S. Pat. No. RE 34,502, the disclosure of which is incorporated herein by reference, describes a catheter having a control handle comprising a housing having a piston chamber at its distal end. A piston is mounted in the piston chamber and is afforded lengthwise movement. The proximal end of the elongated, tubular catheter body is attached to the piston. A puller wire, typically made of stainless steel, is attached to the housing and extends through the piston, through the catheter body and into an off-axis lumen in the catheter tip section. The distal end of the puller wire is anchored in the tip section of the catheter. In this arrangement, lengthwise movement of the piston relative to the housing results in deflection of the catheter tip section.
A known disadvantage of the deflectable catheters is that after deflection, and particularly after repeated deflections in one direction, the tip tends to maintain a residual curve in that direction. In other words, the tip is unable to return to its original straight orientation when the deflecting force is removed. This is a result of the deformable nature of the material of the tip section and particularly of the stainless steel puller wire.